It is often desirable to identify the source of a liquid hydrocarbon, such as petroleum, naphtha, gasoline, diesel fuel, jet fuel, kerosene, lubricant, gas, liquefied gas and the like. Such a need arises for example, in case of suspected fraud, such as theft from pipes, transportation tankers and storage units, intentional or unintentional adulteration, dilution or mixing of fluid from different sources, oil spills or leaks from an uncertain origin to the earth or water, and so forth. The high values as well as evasion of taxation provide lucrative grounds that highly motivate rogue interference with the fluids. By marking the vulnerable liquid beforehand, it is possible to identify at a later stage whether the liquid remained genuinely intact or it was adulterated, diluted or otherwise interfered with.
Methods and systems for marking liquid hydrocarbons are known in the art. The terms “liquid hydrocarbon”, “oil”, “fuel”, “fluid”, and “petroleum”, are synonymously applied herein in their broadest sense, to designate all similar fluids and liquids. The oil is generally marked by a substance which can be later detected, thereby identifying the source of the oil. For example, the substance can be an oil miscible liquid, which is added to the oil, and emits light at distinct wavelengths, when exposed to light or other radiation. A simple dyeing substance is mixed with the oil, thereby changing the color of the oil and allowing the oil to be identified according to the marked color. Alternatively, the marking substance can emit light at an invisible wavelength, wherein the oil is identified by measuring the emitted wavelength by an optical detector. According to other methods, the fuel is marked with an organic compound whose presence is later detected by a spectrometer or a chromatograph. In general, the marker has to satisfy certain criteria pertinent to the specific marked fluid. For example—cost, ease of detection, stability, solubility and compatibility with the fluid (such as flammability with the marked fuel in engines), inertness to air, water and normal soil components, corrosiveness, volatility, and toxicity.
U.S. Pat. No. 5,598,451 issued to Ohno et al., and entitled “Apparatus for Measuring the Sulfur Component Contained in Oil”, is directed to an apparatus for detecting the sulfur component contained in an oil. The apparatus includes a high voltage power supply, an X-ray tube, a filter, a sample cell, an X-ray window, an X-ray detector and a measurement circuit. The high voltage power supply is coupled to the X-ray tube for generating X-rays. The measurement circuit is coupled to the X-ray detector. The filter is located between the X-ray tube and the sample window. The sample cell is located between a sample inlet and a sample outlet and the sample flows through the sample cell. The X-ray window is located in front of the sample cell. The X-ray tube, the filter, the sample window and the X-ray detector are located in such position, that X-rays emitted by the X-ray tube toward the X-ray window and reflected by the X-ray window, strike the X-ray detector.
The X-ray tube includes a target made of Titanium. The X-ray window is made of Beryllium. The sample contains sulfur. X-rays, generated by the X-ray tube and filtered by the filter, strike the sample cell through the sample window. Fluorescent X-rays, which are radiated from the sulfur contained in the sample, strike the X-ray detector. The measurement circuit determines the concentration in weight of the sulfur contained in the sample, by measuring the detected X-ray intensity of the K-shell characteristic X-rays of the sulfur.
U.S. Pat. No. 6,214,624 issued to Barker et al., and entitled “Use of Perfluorocarbons as Tracers in Chemical Compositions”, is directed to a method for marking a liquid medium by a perfluorocarbon tracer. The perfluorocarbon tracer is dissolved, admixed, dispersed or emulsified in the liquid medium. At the detections stage, a sample of the liquid medium is collected on activated carbon, desorbed and passed over a strong oxidizing catalyst, such as a 10-25% V2O2/Al2O3 catalyst, thereby combusting non-perfluorocabonated material. The water is removed from the combusted sample, by employing a semi-permeable membrane, and the combusted sample is introduced into a gas chromatograph equipped with a standard electron capture detector interfaced and a recorder.
U.S. Pat. No. 6,312,958 issued to Meyer et al., and entitled “Method for Marking Liquids with at Least Two Marker Substances and Method for Detecting Them”, is directed to marking liquids with at least two markers, such that the fraudulent liquid is detected, even if the fraudulent liquid is mischievously marked with markers similar to the original ones. Meyer teaches the use of at least two markers having overlapping absorption ranges, which makes possible to use a large number of markers within a given wavelength range. The compounds used by others to misrepresent the original liquid, have to have not just absorption maxima similar to the original markers, but also characteristics similar to the original markers in the rest of the absorption range. Each fraudulent marker can have only one relatively narrow absorption maximum which corresponds with that of one of the original markers. If light sources are used to emit only in the regions of the absorption maxima, then similar fluorescence spectra are likely to result in both cases. However, if light sources are used which emit at wavelengths which the fraudulent markers have no absorption, but at which the original markers have overlapping absorption ranges, then fluorescent light emitted by these markers is detected in the case of original markers, but not in the case of fraudulent markers.
U.S. Pat. No. 5,980,593 issued to Friswell et al., and entitled “Silent Fluorescent Petroleum Markers”, is directed to a method to mark a liquid product by a group of markers and a method to identify a liquid product. The marker is a compound which is synthesized by esterification of an appropriately selected linear or branched C1-C18 alkyl carboxylic acid. According to the patent, C5-C10 alkyl carboxylic acids are employed to mark fuels, because of reduced interference from background fluorescence. The concentration of the marker in the liquid petroleum product is generally at least about 0.25 ppm.
Extraction of the marker from the tagged petroleum product for detection purposes can be performed with a solution composed of 5-60 volume percent of a water miscible, petroleum-immiscible bridging solvent, water, a mineral alkaline source, such as KOH, and/or an alkyl or alkoxy amine. As a field test, a suitable volume of the aqueous extractant mixture is mixed with a suitable volume of the liquid petroleum which is to be tested. If the marker is present in the petroleum product, it will be extracted by the aqueous layer and caused to fluoresce by reaction with the extraction mixture. A hand held ultraviolet light source is used to qualitatively detect the marker. According to this method, it is possible to determine marker levels to within about 5%. As an example, a fuel was tagged with 3 ppm of the marker dissolved in isooctane. The marker was extracted and tested under an ultraviolet lamp, thus providing a blue fluorescent glow, which indicated the presence of the marker.